ETC5523: Communicating with Data

Introduction to web technologies

Lecturer: Emi Tanaka

Department of Econometrics and Business Statistics



Aim

  • Understand the make up of web documents, i.e. HTML, CSS and JS
  • Write basic HTML and CSS with valid syntax
  • Use CSS selectors to apply new styles
  • Integrate CSS and JS to R markdown documents with HTML output

Why

  • Basic web development skills are necessary for customising HTML documents
  • This hard skill will be necessary later for when you are communicating with web documents and web apps

🌐 World Wide Web (WWW)

  • WWW (or the Web) is the information system where documents (web pages) are identified by Uniform Resource Locators (URLs)

  • A web page consists of:

    • HTML provides the basic structure of the web page
    • CSS controls the look of the web page (optional)
    • JS is a programming language that can modify the behaviour of elements of the web page (optional)

🔨 Web Documents are Handy

  • HTML documents are really handy for including interactive elements and supported in almost all computer devices.
  • Naturally, this ties in well with interactive data visualisation.
  • Below is an interactive timeline visualisation of historical developments of HTML/CSS/JS:

So what exactly is
HTML, CSS, and JS?

Hyper Text Markup Language

  • HTML files have the extension .html.
  • HTML files are often rendered using a web browser via an URL.
  • HTML files are just text files that follows a special syntax that alerts web browsers how to render it.

Simple HTML example

simple-example.html 

<html>
<body>
<h1>ETC5523: Communicating with Data</h1>
<h2>Lecturer</h2>
<ul>
<li>Emi Tanaka (Chief Examiner)</li>
</ul>
<h2>Tutor</h2>
<ul>
<li>Weihao (Patrick) Li</li>
</ul>
</body>
</html>

HTML Structure

<html>
<!--This is a comment and ignored by web client.-->
<head>
  <!--This section contains web page metadata.-->
  <title>Communicating with Data</title>
  <meta name="author" content="Emi Tanaka">
  <link rel="stylesheet" href="css/styles.css">
</head>

<body>
<!--This section contains what you want to display on your web page.-->
<h1>I'm a first level header</h1>
<p>This is a paragraph.</p>
</body>
</html>

HTML Syntax

<span style="color:blue;">Author content</span>

Author content

The breakdown of this HTML syntax:

start tag: <span style=“color:blue;”>Author content</span>
end tag: <span style=“color:blue;”>Author content</span>
content: <span style=“color:blue;”>Author content</span>
element name: <span style=“color:blue;”>Author content</span>
attribute: <span style=“color:blue;”>Author content</span>
attribute name: <span style=“color:blue;”>Author content</span>
attribute value: <span style=“color:blue;”>Author content</span>

Not all HTML tags have an end tag

<img height="200px" src="https://tinyurl.com/rlogo-svg">


Some HTML elements

block element: <div>content</div>
inline element: <span>content</span>
paragraph: <p>content</p>
header level 1: <h1>content</h1>
header level 2: <h2>content</h2> (note: only up to 6 levels)
italic: <i>content</i>
emphasised text: <em>content</em>
bold: <b>content</b>
strong importance: <strong>content</strong>
link: <a href=“https://cwd.numbat.space/”>content</a>
insert new line: <br>
unordered list: <ul>
<li>item 1</li>
<li>item 2</li>
</ul>

How these are rendered to the browser depends on the browser default style values, style attribute or CSS…

Cascading Style Sheet (CSS)

  • CSS files have the extension .css and styles also XHTML, plain XML, SVG and XUL.
  • There are 3 ways to style elements in HTML:
    • inline by using the style attribute inside HTML start tag:
    <h1 style="color:blue;">Blue Header</h1>
    • externally by using the <link> element:
    <link rel="stylesheet" href="styles.css">
    • internally by defining within <style> element:
    <style type="text/css"> h1 { color: blue; } </style>

CSS Syntax

<style type="text/css">
h1 { color: blue; }
</style>

<h1>This is a header</h1>

This is a header

The breakdown of the CSS syntax:

selector: h1 { color: blue; }
property: h1 { color: blue; }
property name: h1 { color: blue; }
property value: h1 { color: blue; }

You may have multiple properties for a single CSS selector

h1 {
  color: blue;
  font-family: monospace;
  background: yellow;
}


This is a header

Some CSS properties

<div> Sample text </div>
background color: div { background-color: yellow; }
Sample text
text color: div { color: purple; }
Sample text
border: div { border: 1px dashed brown; }
Sample text
left border only: div { border-left: 10px solid pink; }
Sample text
text size: div { font-size: 10pt; }
Sample text
padding: div { background-color: yellow;
    padding: 10px; }
Sample text
margin: div { background-color: yellow;
    margin: 10px; }
Sample text
horizontally center text: div { background-color: yellow;
    padding-top: 20px;
    text-align: center; }
Sample text
font family: div { font-family: Marker Felt, times; }
Sample text
strike: div { text-decoration: line-through; }
Sample text
underline: div { text-decoration: underline; }
Sample text
opacity: div { opacity: 0.3 }
Sample text

CSS Selector

*    selects all elements
div    selects all <div> elements
div, p    selects all <div> and <p> elements
div p    selects all <p> within <div>
div > p    selects all <p> one level deep in <div>
div + p    selects all <p> immediately after a <div>
div ~ p    selects all <p> preceded by a <div>
.classname    selects all elements with the attribute class=“classname”.
.c1.c2    selects all elements with both c1 and c2 within its class attribute.
.c1 .c2    selects all elements with class c2 that is a descendant of an element with class c1.
#idname    selects all elements with the attribute id=“idname”.

JavaScript (JS)

  • JS is a programming language and enable interactive components in HTML documents.
  • You can insert JS into a HTML document in two ways:
    • internally by defining within <script> element:
    <script>
document.getElementById("p1").innerHTML = "content";
</script>
    • externally by using the src attribute to refer to the external file:
    <script src="myjava.js"></script>
  • You are not expected to be able to do any JS in this course.

HTML outputs with
Rmd documents

---
output: html_document
---
---
output: bookdown::html_document2
---

Inserting CSS in Rmd documents Part 1

  • There is a css engine:
```{css}
h1 { color: red; }
```
  • This inserts the following output into the document:
<style type="text/css">
h1 { color: red; }
</style>
  • If the output is a HTML document then the defined styles will apply to the output document.

Inserting CSS in Rmd documents Part 2

  • If you have an external file, say styles.css, that you define the styles, then most HTML outputs will support this with YAML argument css
---
output: 
  html_document: 
    css: ["styles.css"]
---

or say

---
output: 
  bookdown::html_document2: 
    css: ["styles.css", "custom.css"]
---

Inserting JS into Rmd documents Part 1

  • There is a js engine:
```{js}
document.getElementById("p1").innerHTML = "content";
```

which inserts:

<script type="text/javascript">
document.getElementById("p1").innerHTML = "content";
</script>
  • If you have an external file, say myjava.js, then you can directly insert this in the body of the Rmd file as:
<script src="myjava.js"></script>

Inserting JS into Rmd documents Part 2

If you need to insert at a specific location within the document then you can use includes:

---
output:
  html_document:
    includes: 
      in_header: ["header.html"]
      before_body: ["before_body.html"]
      after_body: ["after_body.html"]
---

where header.html, before_body.html, after_body.html includes the JS code, e.g. 

<script src="myjava.js"></script>
<script type="text/javascript">
document.getElementById("p1").innerHTML = "content";
</script>

Community Web Enhancements

  • Bootstrap is a free open-source CSS and JS that is widely adopted.1
  • jQuery is a widely used JS library for object selection and manipulation.1
  • MathJax is a JS library for displaying mathematics.1
  • Font Awesome inserts icons to web using their CSS.2
  • D3.js is one of the most popular JS library for interactive data visualisation.

☁️ Communication in the Web

  • Hypertext Transfer Protocol (HTTP) functions as the communicator in the Web
  • HTTPS is the secure version of HTTP where communications are encrypted

Warning

Different clients may work differently! E.g. Internet Explorer and Chrome may render the same web page differently.

📋 Web Standard

  • There are 3 major groups that govern the standard for the Web:
    • World Wide Web Consortium (W3C) formed in 1994 maintains the CSS specifications
    • Web Hypertext Application Technology Working Group (WHATWG) formed in 2004 and is the publisher of the HTML and DOM standards
    • TC39 technical committee of Ecma International, renamed from European Computer Manufacturers Association (ECMA) in 1994, maintains the standards for JS
  • These groups consist of Mozilla, Apple, Google, Microsoft and other invited members.

📜 MDN Web Docs LIVE DEMO

https://developer.mozilla.org/

  • Documentation of web standards maintained by the community.
  • Includes status of use:
  • As well as its compatibility with web clients:

Writing HTML

You can play at https://htmltidy.net/

📝 Interactive Cheatsheets

HTML Cheatsheet https://htmlcheatsheet.com/

CSS Cheatsheet https://htmlcheatsheet.com/css/

JS Cheatsheet https://htmlcheatsheet.com/js/

🔎 Inspect Element LIVE DEMO

Below GIF shows interactive use of Inspect Element1 available from the menu in most web browsers when you right click on the web page2:

˜

Week 2 Lesson

Summary

  • We went through the basics of HTML, CSS and JS
  • You should be more comfortable with writing HTML and CSS
  • You learnt how to include CSS and JS into HTML documents created from R Markdown
  • You know the tools to interactively learn HTML and CSS

Resources

ETC5523 Week 2